Perhaps the most common of all damages to a vehicle is windshield damage. Stones and rocks from the roadway are kicked up by vehicle tires and strike the windshield, causing the glass to fracture. Windshields typically include an inner glass layer or plate and an outer glass layer or plate separated by a sheet of tough mylar or other transparent plastic material. Each of the glass layers are highly shatter resistent and even when the outer plate is pitted or cracked, the windshield may be quite serviceable except for the crack being visible. The visible fracture is annoying and can impair the driver's vision of the road. For these reasons, cracked and/or pitted windshields are commonly replaced at a very substantial cost, typically in the hundreds of dollars. (Whereas windshield fractures are of varying types and descriptions, they will often herein be collectively referred to as cracks.)
Recently, developments have been made for repairing windshields having cracked outer glass layers. The concept is quite simple. The crack in the windshield is visible because of ambient air that resides in the openings of the crack. Because air has a different index of refraction than the glass, light is transmitted in a manner different than the glass and becomes visible. A liquid filler material injected into the crack so as to replace the air will make the crack invisible if that liquid has the same index of refraction as the glass. Such a liquid that will harden and bond securely to the glass provides the added benefit of reinstating the strength of the glass and inhibits any spreading of the crack.
A filler material that satisfies the needs of the present invention is a transparent resin identified as "Crack Weld".TM. which is in liquid form until subjected to ultraviolet light. The liquid material is shielded from ultraviolet light (sunlight) until the air in the crack is replaced with the filler material so that the crack is no longer visible. Ultraviolet light is then applied and the filler material cures and hardens.
The concept is simple and the filler material is available. Not so readily available, however, is the apparatus or device to accomplish the task of injecting the filler material into the crack so as to remove or replace the air. The present invention is directed to a device for serving that purpose.
Before explaining devices that have been available heretofore and to which the present invention is an improvement, the reader needs to understand that there are two different kinds of cracks commonly considered for repair by the techniques that will be described. The first is what might be considered as a surface crack. The crack along its entire length is exposed to the atmosphere. By injecting the liquid filler material into the crack, the air is simply crowded out of the crack and thereby replaced. This type of crack does not create a very serious problem for prior devices. However, such damaged windshields are more likely not repairable. If the crack is of the second variety where it is largely formed under the surface with a small hole into the crack, as it frequently is when struck by a small object, simply injecting the filler material into the crack will not get rid of the air which becomes trapped under the surface.
Devices that have been developed for repairing cracks incorporate a mechanism in some respects having the features of an air pump. The small opening into the crack is sealed by the device so as to communicate only with an air chamber or cylinder of the device. A vacuum is drawn to remove air from the crack. The filler material is injected into the device adjacent the opening to the subsurface crack (e.g. through a syringe) and the vacuum is released so that the filler material is drawn into the crack. Whereas the vacuum generating step does not remove all of the air, the process often must be repeated. Because of the relative properties of air versus the highly viscous filler material, air will be gradually withdrawn through the filler material until the air is totally replaced with the filler material and the crack becomes invisible.
Prior patents that function in this manner are U.S. Pat. No. 3,562,366 Sohl 02/09/71, U.S. Pat. No. 3,765,975 Hollingsworth 10/16/73, U.S. Pat. No. 4,132,516 Storey 01/01/79, and U.S. Pat. No. 4,200,478 Jacino 04/29/80.